Characteristics of Interlayer Tunneling Field-Effect Transistors Computed by a “DFT-Bardeen” Method

Theoretical predictions have been made for the current–voltage characteristics of two-dimensional heterojunction interlayer tunneling field-effect transistors (Thin-TFETs), focusing on the magnitude of the current achievable in such devices. A theory based on the Bardeen tunneling method is employed, using wavefunctions obtained from first-principles density functional theory. This method permits convenient incorporation of differing materials into the source and drain electrodes, i.e., with different crystal structure, lattice constants, and/or band structure. Large variations in tunneling current are found, depending on the two-dimensional materials used for the source and drain electrodes. Tunneling between states derived from the center (Γ-point) of the Brillouin zone (BZ) is found, in general, to lead to larger current than for zone-edge (e.g., K-point) states. The differences, as large as an order of magnitude, between the present results and various prior predictions are discussed. Predicted values for the tunneling current, including the subthreshold swing, are compared with benchmark values for low-power digital applications. Contact resistance is considered, and its effect on the tunneling current demonstrated.